Mechanisms of allergic contact dermatitis

Abstract

During the past decade, much has been learned about the pathophysiology of ACD, yet much remains to be determined. Increasing knowledge of the dynamics of percutaneous absorption could result in improved systems for patch testing and might even lead to production of effective barriers creams. A better understanding of the antigenic moiety and of antigen processing by Langerhans cells could lead to reliable in vitro diagnostic tests for ACD. While Langerhans cells, IL-1, IL-2, IFN-γ, and the T-effector circuits have been extensively studied, it is still not clear whether it is Langerhans cell- or keratinocyte-derived IL-1 or both that are crucial in ACD; whether IL-1 acts primarily on T cells or on the antigen-presenting cells; whether other cytokines are involved in the reaction (tumor necrosis factor, keratinocyte-derived growth factor); what the exact relationships are among T-effector, T-memory, and other T-helper cells; what the functions of mast cells and basophils are in the allergic reaction; and how the regulatory circuits (including prostaglandins and eicosanoids) affect the outcome of ACD. Delineation of the complex interactions among Langerhans cells, T cells, and effector cells and their various soluble mediators should further our understanding of those factors that enhance or diminish immune responsiveness. Further insight into the immunologic mechanisms of ACD will lead not only to more sophisticated treatment for ACD, but also to a better understanding of the cell-mediated events of cutaneous viral replication, organ transplantation, and tumor growth.